The present invention relates to a spray method and a spray device, particularly for the spray-coating of articles with powder, in which at least two different spray materials are fed via separate feed lines only one selected spray material being discharged to a spray apparatus at one time via a discharge conduit which is common to all of the feed conduits.
In a known device of this type (German Unexamined Application for Patent No. 22 37 507), the feed conduits must be rotated with respect to the common delivery conduit to connect a selected conduit. The known device serves for the spray-coating of articles with powder. In this case, there occur problems as to sealing and difficulties in the avoiding of undesired deposits of powder in the transition region between the feed conduits and the delivery conduit. These difficulties increase when the sealing surfaces become worn after a certain period of operation.
The powder is conveyed by propellant gas and passes downstream of the said known device, for example, to a powder spray gun such as known from German Pat. No. 20 30 388. From that German patent it is also known to electrostatically charge the sprayed powder so that it is attracted by the article to be coated and adheres better to it.
Pipe switches such as known from German Unexamined Application for Patent No. 1 481 189 and from German Provisional Patent No. 1 245 847 have not been used up to now for spraying, particularly for the spray-coating of articles with powder. This may be due to the entirely different technical fields. Other important reasons may be that the known pipe switches are traversed in the direction opposite to that of the invention and that there is a danger that the spray material would deposit in them. Such deposits might pass during the spray-coating as clots of color onto the article to be coated. Again, it might not be possible to remove the clots during ordinary cleaning procedures, in which case they would then mix with a subsequently employed coating material, which would lead to defects in coating or to the spraying device becoming clogged after some time. Spray-coating, particularly with powder, is a very sensitive procedure, since the mixing or even very small particles of a different material with the material which is being applied at the time leads to such extensive defects in coating that the coating is unusable.
These sealing problems and a moving of the conduit or parts of the conduit as well as a mixing of different spray materials upon change from one spray material to another are to be avoided by the present invention. Furthermore the invention solves the problem of simplifying the spraying process and the apparatus necessary for it and of making it more economical and diversified in use.